Harden SSLv2-supporting servers against Bleichenbacher's attack.

Harden SSLv2-supporting servers against Bleichenbacher's attack.

There is no indication that the timing differences are exploitable in
OpenSSL, and indeed there is some indication (Usenix '14) that they
are too small to be exploitable. Nevertheless, be careful and apply
the same countermeasures as in s3_srvr.c

Thanks to Nimrod Aviram, Sebastian Schinzel and Yuval Shavitt for
reporting this issue.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(cherry picked from commit ae50d8270026edf5b3c7f8aaa0c6677462b33d97)